[T3] Why is it that when I got my 73 SB I never had to turn thekey several times to prime the system .

[William J]

Jim:

 I think I understand the fuel pump now . Let me know if I have this right.

 The so called check valve if it fails one way no fuel output and the other 
way it won't hold pressure in the system after shut down . In the later this 
means to me if it won't hold pressure after shut down this would be every 
time the car is started and shut down one would need to cycle the key even 
if it were a short trip IE the pressure would just drop to zero right after 
shut down or slowly bleed down so the car may start right up depending over 
all on how fast the pressure drops to zero.

 There was some spec on how long the pressure would hold if all if working 
well wasn't there? And a certain amount of pressure needed to just turn the 
key and it would start . The 1.5 seconds the pump relay runs the pump if 
everything is well should bring the pressure back up for one turn of the key 
start up as long as there is a certain amount of pressure still in the lines 
. Also after shut down when the starting is engaged at the same time the 
fuel pump relay is so no need for the 1.5 second time out .



 This hot soak fuel boil is what forces the liquid fuel back through the 
pump leaving just vapor because of the pressure difference 30 PSI line 
pressure  and 20 PSI is what it takes to force the fuel back through the 
pump leaving vapor only due to the so called check valve thus the key cycle 
deal  or added switch.

 what I still can't get past is why I never had this hot fuel soak and vapor 
and never needed to cycle the key before.

 As it is now the car can sit after hot shut down over night and will start 
in the morning yet I don't drive everyday . I can drive it and shut it down 
and it will fire right up even after a 10 mile trip in hot weather after 
sitting over an hour. I can drive a mile or more and it always starts . I've 
driven it 4 miles 4 starts park in a hot garage and then get in and it fires 
right up.

 I have a momentary contact toggle switch rated at 25 amp figured I'd just 
wire it fused  side of  a hot all the time fuse tied to the fuel pump hot 
lead where it connects to the pump relay. Pump has it's own ground not 
dependant of relay.

----- Original Message ----- 
From: "Jim Adney" <jadney at vwtype3.org>
To: <type3 at vwtype3.org>
Sent: Friday, August 04, 2017 6:25 AM
Subject: Re: [T3] Why is it that when I got my 73 SB I never had to turn 
thekey several times to prime the system .


> On 3 Aug 2017 at 15:12, William J wrote:
>
>> If the check valve goes completely then the
>> pump will not put out pressure is this true?
>
> There are at least 2 ways in which the check valve can fail. If it fails 
> one of
> those ways it can block the pump outlet, preventing any gas from getting 
> out
> of the pump. If it fails the other way, the pump will still put out gas at
> pressure, but it won't hold pressure in the line after shutdown.
>
> Our pumps are now old enough that they are all starting to fail one way or
> another. I can usually rebuild them, giving them another few decades of 
> life.
>
> It's very important that the "overflow" hose under the RF fender be 
> intact,
> because leaks there let water and dirt into the gas system. Since the OE
> hoses are always cracked by now, and the OE hose is NLA from VW, I've
> developed a kit to repair it. So far, I've not seen or heard of any of my 
> kits
> failing, and they've been out there for about 10 years, which is about 
> 3x - 4x
> longer than the OE hoses tended to last for me. These were always a weak
> spot in the '68-73 Type 3 design.
>
> -- 
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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